Doubles trim epiphany

[AJ]

The main problem is balancing around the centre of gravity. Everything that influences the centre of gravity is important. Shape of the wing, place of weight, air in drysuit, muscle tension, etc. Changed back plates, wings, shifted tanks, etc. I strugled around 200 dives until one day I found I had solved the puzzle. Now I can completely relax, just breathe and stay perfectly still. It's a combination of my rig config and skills that makes this possible.

 

[lowviz]

Okay, I know that some of you that read this are going to end up thinking "duh! It took you THIS long to figure that out?!?!?" But, well, yes, it did.

No surprise to me. Took me even longer. Wings are different, the manufacturers only yap about what will sell. Absolutely no reference to the basic physics of the wing.

I've had or have 4 doubles wings:

Seven. Forever in search of the Holy Grail. See pic.

Comments to enhance my understanding further or correct me where I've come to a wrong conclusion would be VERY welcome!

I'll unlock this for a couple of days. I can determine the forces needed to hold a wing at any reasonable angle. What made it all work was the chain that hangs down to the bottom of the pool. Without it, the rig was either at the surface or sunk. Ultra stable with the chain.

See attached pic. The "parallel bar" mates with the rack seen balancing on it. The rack bolts to my backplate. Now I have a datum. A zero. Half a breath, DS, Thermals, hood, and mask. I know where I balance in either frog or flutter. No BS "skills" apply. Just physics. I love to dive a conglomeration of shyT. No reason that I can't hit the water in perfect balance. Just follow the spreadsheet.



AJ is dead nuts on...

 

[stuartv]

No surprise to me. Took me even longer. Wings are different, the manufacturers only yap about what will sell. Absolutely no reference to the basic physics of the wing.

Seven. Forever in search of the Holy Grail. See pic.

I'll unlock this for a couple of days. I can determine the forces needed to hold a wing at any reasonable angle. What made it all work was the chain that hangs down to the bottom of the pool. Without it, the rig was either at the surface or sunk. Ultra stable with the chain.

See attached pic. The "parallel bar" mates with the rack seen balancing on it. The rack bolts to my backplate. Now I have a datum. A zero. Half a breath, DS, Thermals, hood, and mask. I know where I balance in either frog or flutter. No BS "skills" apply. Just physics. I love to dive a conglomeration of shyT. No reason that I can't hit the water in perfect balance. Just follow the spreadsheet.

View attachment 395249

AJ is dead nuts on...

I'm not sure what "I'll unlock this" means. You talking about security on the Vimeo video?

The concept is awesome. If I'm understanding your gist, you are basically saying that if you get the rig by itself to be neutral with respect to trim, then when you wear it, you will be neutral (assuming you are neutral with respect to trim by yourself).

Am I picking up what you're putting down here?

If so, why do you need to go to all that trouble with the bar, etc? Why can't you just get it in the pool and hold it horizontal while you rest weights on the tank to get it to balance horizontally? One you figure out what you need and where, then use cam bands and trim pockets to affix them.

I like the idea! But, now I'm wondering, what if you are diving dry and need more weight and you want it to be ditchable, so you want to put it on a belt? If you put on a weight belt, then you are probably no longer neutral (with respect to trim). Ditto for if you have negative fins (like my Hollis F1s).

So, how you figure out how to adjust the rig to compensate for a diver who is not neutral (with respect to trim)? Wouldn't you be back to just putting it on and trial-and-error?

 

[lowviz]

... You talking about security on the Vimeo video?

Yes.

... If I'm understanding your gist, you are basically saying that if you get the rig by itself to be neutral with respect to trim, then when you wear it, you will be neutral (assuming you are neutral with respect to trim by yourself).

Not exactly. Think of it as reducing the wing to a force (lift at various amounts of inflation) and then determining the point of application of that force to keep the wing at whatever trim you want. The point of application is recorded as an offset from the top hole in the wing. You get a glimpse of the weighted slider at the end of the vid. it runs in a track and accepts weight plates. You read the offset directly using an attached ruler.

... If so, why do you need to go to all that trouble with the bar, etc?

I use the same thermals, DS, backplate, and mask. So I need to know where I balance with a fully compressed suit. (shop vac) I'm buoyant, pony on the pool floor with #50 wieght plates on each upright. The bar holds me under while I find the right slot in the 'rack' that will hold me in trim. I know where I balance and it is marked on my BP. I keep picking up lead until I'm neutral. 10/11 of that weight is my true buoyancy.

... If you put on a weight belt, then you are probably no longer neutral (with respect to trim). Ditto for if you have negative fins (like my Hollis F1s).

Yes. But now a W/B is just another force (down) at some offset from my zero. Same for everything else. It all reduces to a force at a distance from my zero.

... So, how you figure out how to adjust the rig to compensate for a diver who is not neutral (with respect to trim)? Wouldn't you be back to just putting it on and trial-and-error?

No. Add everything up and you will be left with an error. Usually a bubble in the DS will do it. That is easy too. Add however many pounds to the weight that keeps me neutral, add air to the suit to get back to neutral and find the new slot in the rack. Again everything including the suit bubble reduces to a force and a point of application.

 

[stuartv]

Yes.

Not exactly. Think of it as reducing the wing to a force (lift at various amounts of inflation) and then determining the point of application of that force to keep the wing at whatever trim you want. The point of application is recorded as an offset from the top hole in the wing. You get a glimpse of the weighted slider at the end of the vid. it runs in a track and accepts weight plates. You read the offset directly using an attached ruler.

I get it now. I couldn't really tell what your device was doing from that video. Interesting. If you lived closer, I'd ask to come over and have a session with your Trim Machine.

 

[kelemvor]

Holy cow, @lowviz takes trim seriously!

 

[lowviz]

More like total frustration.

Way back when I decided to shake off my NE wreck diving bad habits, I found trim in frog position to be near impossible. Got the same message from everyone, it is all due to your form. It wasn't. One of the secrets of DIR/GUE is to get to a stable rig and don't mess with it. Fine, but I don't dive like that. I love diving whatever I can get my hands on. It is fun to dive different gear. I just bought a sweet SP Classic jacket BC.

20 dives before you are truly tuned in? Finding Proper Trim
Quoted from the above link:
"It often takes new divers about 20 dives or so to get comfortably weighted with the right amount of ballast, but because trim issues are less conspicuous, divers can go for years without realizing them." Yep.

Every time I make a big change, it takes 20 dives to dial it in?!! Roger that. A two hour drive for a max of three dives on a boat that costs almost $200US all told?

I have a decent metal shop and welding machine in the basement. I'll take any excuse to visit my local metal wholesaler.

Trim is not intuitive. A camera is mandatory. My trim is improving to where it is no longer the deal-breaker when I'm overtasked. That took a hell of a lot of work.

So it all comes down to physics, but you get a wonderful break. All buoyancy forces are vertical. Sink or float. Sum them and fix the error.

All rotational forces operate around your balance point. Force times distance. So yes, you can throw a rig together on paper, do the math, and hang there like one of the cave butterflies when you splash.

@stuartv we aren't that far from each other. I'll loan you the lot anytime you like...

 

[MichaelMc]

I can determine the forces needed to hold a wing at any reasonable angle. What made it all work was the chain that hangs down to the bottom of the pool. Without it, the rig was either at the surface or sunk. Ultra stable with the chain.

I do not really understand the rig (contraption, as distinct from BP/W). From motion in the video, it appears the PB/W is not attached to the rig, and thus the chain to the bottom. Are the white cylinders big PVC pipes? Do you have a wider angle picture of the whole thing in water? How does this differ from say attaching the chain to a rod screwed between the backplate holes with several attachment points along the rods length?

I get the idea that a trimmed BP/W applies no torque(?) to the ‘rigid’ divers body, just a point weight at some distance from the divers existing center.

I have not measured my trim, but one way I make small gear compensations is with a few weights I can move up and down my harness straps, or into my belts. 1 lb. weights with bolt snaps and a few inner tube bands as movable attach points and to pull the weight tight to the straps. My kludge for in water static adjustment.

 

[kelemvor]

More like total frustration.

Way back when I decided to shake off my NE wreck diving bad habits, I found trim in frog position to be near impossible. Got the same message from everyone, it is all due to your form. It wasn't. One of the secrets of DIR/GUE is to get to a stable rig and don't mess with it. Fine, but I don't dive like that. I love diving whatever I can get my hands on. It is fun to dive different gear. I just bought a sweet SP Classic jacket BC.

20 dives before you are truly tuned in? Finding Proper Trim
Quoted from the above link:
"It often takes new divers about 20 dives or so to get comfortably weighted with the right amount of ballast, but because trim issues are less conspicuous, divers can go for years without realizing them." Yep.

Every time I make a big change, it takes 20 dives to dial it in?!! Roger that. A two hour drive for a max of three dives on a boat that costs almost $200US all told?

I have a decent metal shop and welding machine in the basement. I'll take any excuse to visit my local metal wholesaler.

Trim is not intuitive. A camera is mandatory. My trim is improving to where it is no longer the deal-breaker when I'm overtasked. That took a hell of a lot of work.

So it all comes down to physics, but you get a wonderful break. All buoyancy forces are vertical. Sink or float. Sum them and fix the error.

All rotational forces operate around your balance point. Force times distance. So yes, you can throw a rig together on paper, do the math, and hang there like one of the cave butterflies when you splash.

@stuartv we aren't that far from each other. I'll loan you the lot anytime you like...

Do you need to compensate for the trim of your body or are you doing that via skill and merely trimming out the rig? I was just thinking that if you could make yourself neutral in the water while naked, your body its-self might not be perfectly trimmed. In which case it might be better to have the bcd or weights or whatever compensate for the lack of perfectly even buoyancy throughout the body.

 

[lowviz]

I do not really understand the rig (contraption, as distinct from BP/W). ...//...

Muppet Labs is closed for the season due to ice but I'll explain it topside. See pic.


Starting at the top, see the two sealed flotation tubes banded to a stainless steel channel? Frame is welded to channel. Notice the two bolts at 11" spacing also welded to channel. That is how you attach the wing.

Next is the goniometer. (fancy for measures angles) Pick the trim angle you want and pin it to that setting. Done.

Now to balance out the rig U/W. See the two 4# weight belt weights? On is on either side of the "teeter-totter". The whole collection of weight is applied via a small rod to an exact point on the frame. It takes several weights to sink the rig. The reason for the teeter-totter is that it now doesn't matter how your weights are distributed on the bar, all the weight is applied to the same spot on the frame. The metal just about the fulcrum is a clamp. You lock the teeter-totter in place with the cap bolt. That makes fine adjustment a pain. Thus the lead slider above the teeter-totter.

The two bump guards at the bottom of the frame are short pieces of high vacuum hose stuck onto two pins.

The heavy chains make it all work. Add weights until one or two links of each chain are lying on the pool bottom. The weight of those links are now gone, the rig does not sense it. However, if the rig begins to float, it picks up the added weight until it regains balance. Adjust the kinkless index chain so that it just touches the bottom. The rig is neutral and in trim.

So now look at, say, 5 pounds of wing inflation. Add 5 pounds to the slider and the rig sinks. Inflate the wing until the index chain is again just at the pool floor. Move the slider until you get the trim that you want. The slider tells you where the force is applied with respect to one of the bolts. See pic.



Now for each trim angle, you can make a graph of lifting force and point of application.

Do you need to compensate for the trim of your body or are you doing that via skill and merely trimming out the rig? ...//...

No skills. All physics.

The basic system that I start with (and add everything to) is me, undergarments, dry suit, bare backplate, and mask. No fins, no tank, no clip-ons. They all get figured separately. That balance point gets marked on my BP and everything relates to there. You have to convert the offset on your wing (from one bolt or the other) to the zero on your BP. Just a subtraction...